/**

 * Definition for a binary tree node.

 * struct TreeNode {

 *     int val;

 *     TreeNode *left;

 *     TreeNode *right;

 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}

 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}

 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}

 * };

 */

class Solution {

public:

    string tree2str(TreeNode* root) {

        string str;

        if (root == nullptr)

            return str;

        str += to_string(root->val);

        if (root->left || root->right) {

            str += '(';

            str += tree2str(root->left);

            str += ')';

        }

        if (root->right) {

            str += '(';

            str += tree2str(root->right);

            str += ')';

        }

        return str;

    }

};